Services supported by third generation Code Division Multiple Access (CDMA) systems have been provided for mobile communication systems for cellular phones and so on. Under these circumstances, the 3rd Generation Partnership Project (3GPP) is working on Long Term Evolution (LTE) that achieves a much higher data-rate. Now, 3GPP is confronted with hurdles of how to speed up transfer-rates and how to reduce transmission delays.
When a user equipment moves from one location to another location while in service, a base station that communicates with the user equipment performs a handover operation according to the reception condition at the user equipment. In a hard handover that is mainly applied to a packet switching system, a line between the user equipment and a source base station (handover source base station) communicates with the user equipment until the relocation is disconnected and a line between the user equipment and a target base station (handover target base station) that is to communicate with the user equipment is connected.
In the hard handover scenario, the user equipment obtains system information on the target base station immediately before the handover. Accordingly, the handover can be carried out in a short time.
On the other hand, an interruption of user data transmission during the handover causes a transmission delay. Moreover, packet data may be lost in the interruption. In such a case, the lost packet data has to be resent in an end-to-end manner and recovered. This may further increase the transmission delay.
It would be advantageous to reduce the transmission delay during handover in the mobile communication by shortening the transmission interruption time during handover and to prevent the packet data loss in the interruption.